Going back to the first post of this thread...
Just because there are only middle seats left on the seat map does not mean you are guaranteed to be sitting in a middle seat on the plane.
If it's more than a day before the flight, you won't see the last six rows at all. The day before (or 24 hours before, something like that), the last six rows open up for assignment.
Furthermore, with no-shows, you may be able to get a better seat at the gate.
Changing airlines just because of the advance seat assignment map is overkill. The same thing will happen with JetBlue or any airline (except Southwest, which doesn't have advanced seat assignments).
[This message has been edited by JS (edited 02-06-2003).]